He was born in a wealthy merchant family in the Lower Styrian town of Šoštanj, then part of the Austrian Empire.
Josip grew up in a nationally indifferentiated environment; although his mother tongue was German, he was fluent in Slovene since childhood.
[2] He attended the prestigious First Celje Grammar School, where he became involved in the Slovene national revival.
In 1868, he co-founded the newspaper Slovenski narod, which became the herald of Slovene liberalism until the dissolution of the Austro-Hungarian Empire.
Vošnjak was also a prolific author; he wrote many political articles and essays, as well as plays and short stories.